This invention relates to mixing valves and in particular to mixing valves for mixing steam and water.
A typical and common installation where blending of steam with cold water to provide a supply of hot water is used is in the food processing industry where there is a frequent need to wash equipment with hot water at about 80.degree. C.
This is most conveniently done with a hot water hose gun which is supplied with its hot water from a mixing valve. Popular hose guns have a flow on/off trigger for starting and stopping the draw-off of hot water from the mixing valve and means for adjusting the spray pattern.
Previously thermostatic mixing valves have been used to provide the hot water supply to the hose gun. These valves employ a proportioning valve responsive to the hot water temperature for controlling both the steam and the cold water flow so as to maintain the temperature of the hot water substantially constant.
A disadvantage of such valves is that on stopping the water flow they do not completely shut-off the steam flow which can result in the next draw-off of hot water starting with a violent burst of steam which can be dangerous.
A further disadvantage of such valves is that they are generally noisy in operation varying from a deep grumbling to a screeching sound due to mixing of the steam and cold water in a large internal chamber giving rise to a continuous succession of steam implosions. Such steam implosions can also render the mechanism unsuitable making the valve unreliable in operation. Seizure of the mechanism is also a problem.
It is an object of the present invention to provide a mixing valve for mixing steam and water which mitigates at least some of the disadvantages of thermostatic mixing valves above discussed.